High-power LED, by virtue of its advantages of high efficiency, energy conservation, environmental protection, long service life and high reliability, has become a new generation of lighting source and are gradually replacing conventional incandescent lamps and fluorescent lamps etc. With improvement of performances and reduction of production cost, application areas of high-power lighting LEDs have expanded from screen backlight sources and brightness insensitive landscape lightings to general white lighting. On the other hand, drive integrated circuits matched with high-power LED have been considerably developed due to the increasing popularity of the high-power LED applications. Therefore, it is particularly critical to design an efficient and reliable LED lighting drive circuit.
In order to improve the efficiency of the power grid, power factors of lighting devices have been paid more and more attention. Power factor of a lighting device is optimal when an input current of the lighting device varies in a sinusoidal form with voltage of the commercial electric supply. In addition, since a luminous intensity of an LED is proportional to a current passing through the LED within a certain range, in order to ensure the service life and the lighting effect of LED lights, the current passing through the LED is required to be within a certain range and be kept at a constant effective value.
A conventional LED lighting drive circuit generally employs a bulky transformer to transfer power, which takes much space. Moreover, it employs high-voltage electrolytic capacitors with polarities, and the lifetime of the elements will be dramatically shortened after a period of operation, resulting in poor reliability of the product.
With respect to the above defects of the conventional LED lighting drive circuit, there is a demand to develop an LED drive circuit without a transformer for converting power and high-voltage electrolytic capacitors, while having a high power factor.